Shankar G. Aggarwal

Optical properties of accumulation mode, polluted mineral dust: effects of particle shape, hematite content and semi-external mixing with carbonaceous species

ABSTRACT The morphology, mixing state and hematite content of polluted mineral dust are not well accounted in the optical models and this leads to uncertainty in the radiative forcing estimation. In the present study, based on the morphological and mineralogical characterisation of polluted dust, the three-sphere, two-sphere and two-spheroid model shapes are considered. The optical properties of the above model shapes are computed using Discrete Dipole Approximation code. The single scattering albedo, ω 0, was found to vary depending on hematite content (0–6%) and model shape. For the two-sphere BC-mineral dust system, hematite was found to be a dominating absorber compared to that of black carbon as the R BC/R dust decreases. The ω 0 of the polluted dust system is larger if polluted dust is considered as pure dust spheroid (with 4% hematite) while smaller value is observed for Q ext. Among all the systems, the ω 0 of BCBCD (two BC spheres attached to one dust sphere) system showed the maximum departure (40 and 35% for polluted dust with 0 and 6% hematite, respectively) from that of pure dust spheroid with 0 and 6% hematite. For the Asian region (pollution-prone zone), the modelled polluted dust optics will help to trace the optical and radiative properties of dust.

Comparison of experimental and modeled absorption enhancement by black carbon (BC) cored polydisperse aerosols under hygroscopic conditions.

The quantification of the radiative impacts of light absorbing ambient black carbon (BC) particles strongly depends on accurate measurements of BC mass concentration and absorption coefficient (β(abs)). In this study, an experiment has been conducted to quantify the influence of hygroscopic growth of ambient particles on light absorption. Using the hygroscopic growth factor (i.e., Zdanovskii-Stokes-Robinson (ZSR) approach), a model has been developed to predict the chemical composition of particles based on measurements, and the absorption and scattering coefficients are derived using a core-shell assumption with light extinction estimates based on Mie theory. The estimated optical properties agree within 7% for absorption coefficient and 30% for scattering coefficient with that of measured values. The enhancement of absorption is found to vary according to the thickness of the shell and BC mass, with a maximum of 2.3 for a shell thickness of 18 nm for the particles. The findings of this study underline the importance of considering aerosol-mixing states while calculating their radiative forcing.

Quantification of ziram and zineb residues in fog-water samples

The present paper describes the extractive quantification of zinc-dithiocarbamate fungicides, i.e. ziram (zinc bis-dimethyldithiocarbamate) and zineb (zinc ethylene-1,2-bis-dithiocarbamate) in fog-water samples. The method is based on the releasing of equivalent amount of zinc from the fungicides and its subsequent determination by visible spectrophotometry or by flame-atomic absorption spectrometry (flame-AAS). For spectrophotometry, the sample contained up to 48mug of ziram and 42mug of zineb was first equilibrated with chloroform. The recovery results show that only ziram content was extracted into chloroform. Then, the sample was treated with NH(4)SCN and surfactants (i.e. CPC and TX-100) solutions, and extracted with toluene to remove interference of inorganic zinc and other metal ions, if present in the sample. The residue was further used for zineb determination. The chloroform extract and residue were then digested separately with nitric acid to release Zn(II), which were then analyzed spectrophotometerically with 4-(2-pyridylazo)-resorcinol in the micellar medium (TX-100) for the determination of ziram and zineb, respectively. The complex shows lambda(max) at 495nm. The molar absorptivity in terms of ziram/zineb was determined to be (8.05) x 10(4)Lmole(-1)cm(-1). The detection limits for ziram and zineb were calculated to be 20 and 21mugL(-1) (with R.S.D. < 1.5%), respectively. Whereas, the optimum concentration ranges were 0.08-1.6 and 0.07-1.4mgL(-1), respectively. Alternatively, the Zn contents present in chloroform extract and in residue were directly analyzed using flame-AAS without undergoing the digestion procedure, and ziram and zineb were determined, respectively. The optimum concentration ranges were 0.9-4.8 and 0.8-4.3mgL(-1), while the detection limits were calculated to be 145 and 144mugL(-1), respectively with R.S.D. < 2.5%. The methods are free from interference of almost all ions [including Zn(II)] and other dithiocarbamate pesticides, which can commonly associate with ziram/zineb in fog-water.

Acidification of Surface Water in Central India

The results of the seasonal analysis of the chemistry of rain, fog and surface water of central India for the two years: June 1996 to May 1998 are presented. A total of 636 rain water samples, 146 fog water samples and 226 surface water samples of 8 locations: namely, Ambikapur, Baikunthpur, Korba, Bilaspur, Raipur, Bhilai, Dallirajhara and Kanker, from different sites were collected for the present study. This paper documents the occurrence of acidic rain and fog events and their effect on surface water pH and aquatic life in central India. Most of the rain and fog water samples collected from Baikunthpur and Korba sites were found to be acidic in nature (i.e. pH < 5). The volume weighted mean pH of rain and fog water samples of these sites was 4.8 and 4.4 with lowest pH 4.4 and 4.0, respectively. However, samples from Ambikapur, Bilaspur, Raipur and Bhilai were slightly acidic and their pH values were always around 5.8. One reservoir (mean pH 5.8) and two stop dams (mean pH 4.4 and 4.2) in Baikunthpur area were found to be acidic. The effect of acidification of water on metal-accumulation in muscles of fishes was studied. Concentrations of Al, Hg, Mn, Cd and Pb were higher in fish from acid, than from less acid waters. Causes of acidification of the atmospheric water and surface water are critically discussed.

Molecular Markers of Secondary Organic Aerosol in Mumbai, India

Biogenic secondary organic aerosols (SOA) are generally considered to be more abundant in summer than in winter. Here, polar organic marker compounds in urban background aerosols from Mumbai were measured using gas chromatography-mass spectrometry. Surprisingly, we found that concentrations of biogenic SOA tracers at Mumbai were several times lower in summer (8-14 June 2006; wet season; n = 14) than in winter (13-18 February 2007; dry season; n = 10). Although samples from less than 10% of the season are extrapolated to the full season, such seasonality may be explained by the predominance of the southwest summer monsoon, which brings clean marine air masses to Mumbai. While heavy rains are an important contributor to aerosol removal during the monsoon season, meteorological data (relative humidity and T) suggest no heavy rains occurred during our sampling period. However, in winter, high levels of SOA and their day/night differences suggest significant contributions of continental aerosols through long-range transport together with local sources. The winter/summer pattern of SOA loadings was further supported by results from chemical transport models (NAQPMS and GEOS-Chem). Furthermore, our study suggests that monoterpene- and sesquiterpene-derived secondary organic carbon (SOC) were more significant than those of isoprene- and toluene-SOC at Mumbai.

Specific determination of ferbam residues in fog-water

A specific method for the determination of a fungicide, i.e. iron(III) dimethyldithiocarbamate (ferbam) in fog-water samples is described. The method is based on the releasing of equivalent amount of iron from the fungicide and subsequently determination by spectrophotometrically or by flame-atomic absorption spectrometrically (flame-AAS). The fungicide was extracted with chloroform/toluene from the samples and digested with nitric acid. For spectrophotometric determination, the solution was then treated with ammonium thiocyanate solution in presence of the surfactants and absorbance was measured at 475 nm. Whereas, the digested solution was directly applied for flame-AAS determination of ferbam. The molar absorptivity in terms of ferbam was determined to be (3.49)x10(4) l mol(-1) cm(-1). The detection limits for spectrophotometric and flame-AAS methods were calculated to be 62 and 111 ppb ferbam (R.S.D. <1 and <3%), respectively. Whereas, the optimum concentration ranges for the analysis of ferbam are 4-120 and 1.5-55 mug in final volume, respectively. The methods are freed from interference of almost all ions [including Fe(II) and Fe(III)], which can commonly associate with ferbam in fog-water. The methods have been successfully applied to fog samples collected from agriculture sites of Raipur (central India).

Final report on APMP.QM-S5: Essential and toxic elements in seafood

The supplementary comparison APMP.QM-S5 was undertaken to demonstrate the capability of participating national metrology institutes (NMIs) and designated institutes (DIs) in measuring the contents of the incurred essential elements (iron and zinc) and toxic elements (total arsenic and cadmium) at ?g/g levels in a test sample of dried shrimp by various analytical techniques. At the APMP TCQM Meeting held in Pattaya, Thailand in November 2010, Government Laboratory of the Government of the Hong Kong Special Administrative Region (GLHK) proposed this APMP supplementary comparison. The proposal was further discussed and agreed upon at the CCQM Inorganic Analysis Working Group Meeting held in Paris in April 2011. GLHK was the coordinating laboratory for the supplementary comparison. For enhancing the collaboration amongst specialized regional bodies in Asia-Pacific and to help build the laboratory capacity of NMIs/DIs from developing economies, the reference values of the supplementary comparison are used for evaluation of performance of participants of an APMP proficiency testing programme (APMP PT 11-01), an Asia-Pacific Laboratory Accreditation Cooperation proficiency testing programme (APLAC T082) and an Asia-Pacific Economic Co-operation proficiency testing programme (APEC PT), which were concurrently run using the same testing material as in APMP.QM-S5. The supplementary comparison serves to facilitate claims by participants on the Calibration and Measurement Capabilities (CMCs) as listed in Appendix C of the Key Comparison Database (KCDB) under the Mutual Recognition Arrangement of the International Committee for Weights and Measures (CIPM MRA). A total of 18 institutes registered for the supplementary comparison and all of them submitted their results. Most of the participants used microwave acid digestion methods for sample dissolution. For the instrumental determination, a variety of techniques like ICP-MS, ICP-OES, INAA and AAS were employed by the participants. For this supplementary comparison, inorganic core capabilities have been demonstrated by concerned participants with respect to methods including ICP-MS (without isotope dilution), ID-ICP-MS, ICP-OES, INAA and AAS on the determination of total arsenic, cadmium, iron and zinc in a matrix of seafood. Main text. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the APMP, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Effects of chemical composition and mixing state on size‐resolved hygroscopicity and cloud condensation nuclei activity of submicron aerosols at a suburban site in northern Japan in summer

Ambient hygroscopic properties, numbers of size-segregated cloud condensation nuclei (CCN) at different supersaturations (0.1%–0.8%), and the chemical composition of submicron particles were simultaneously measured at a suburban site in northern Japan in summer. Two distinct periods with different growth factors (GF), CCN activation diameters, and chemical compositions were observed. The data suggest that internally mixed sulfate aerosols dominated the accumulation size mode in relatively aged aerosols during the first period, whereas particles observed during the latter periods showed external mixing dominated by organics, which was linked to low hygroscopicity and CCN activity. In particular, the higher loading of water-soluble organic matter (WSOM; ~60% of OM by mass) with increased WSOM/sulfate ratios corresponded to a low hygroscopicity parameter derived from the CCN measurement (κCCN = 0.15 ± 0.02) at a dry diameter (Ddry) of 146 nm. The results suggest that WSOM, likely dominated by the influence of biogenic sources, contributed to reducing the hygroscopicity and CCN activation at this particle size. Temporal variations in the number concentrations for low GF mode at Ddry = 49.6 nm were similar to those in the elemental carbon (EC) concentration, suggesting that EC contributed to reducing hygroscopicity at this smaller size. Our results suggest that chemical composition and mixing state are important factors controlling the hygroscopicity and CCN activation of submicron particles. These results provide useful data sets of size-resolved sub- and supersaturated hygroscopicity, and highlight the importance of the abundance of OM relative to sulfate in predicting the effects on climate change.